A method for analyzing security performance of star-ris assisted terahertz underwater wireless optical communication

Abstract

The application discloses a safety performance analysis method for a terahertz underwater wireless optical communication system assisted by a simultaneously transmissive and reflective reconfigurable intelligent surface (STAR-RIS), the method comprehensively considers a hardware damage and a jammer-assisted scenario with practical significance, gives an expression of system safety rate and an approximate closed-form expression theoretical calculation method, can avoid the need for evaluating the rate performance by using a Monte Carlo simulation, and greatly simplifies the safety rate calculation; simulation results show that the performance analysis method is effective for evaluating the safety performance of the system, and the STAR-RIS can effectively improve the system safety rate.

Description

Technical fields:

[0001] This invention belongs to the field of wireless mobile communication and relates to a performance analysis method for mobile communication systems. In particular, it relates to a security performance analysis method for a reconfigurable smart metasurface STAR-RIS assisted terahertz underwater wireless optical communication THz-UWOC that can simultaneously transmit and reflect light. Background technology:

[0002] With the exponential growth of wireless communication traffic, the upcoming sixth-generation mobile communication is expected to provide data rates exceeding 1Tbps, serving more users and meeting diverse business needs. Terahertz (THz) communication refers to an emerging communication technology that utilizes THz waves for information transmission. Traditional communication spectrum resources are becoming increasingly scarce, and THz communication offers a new approach and technical path to solve this problem. Although THz waves have many advantages, they face significant free-space path loss and atmospheric molecular absorption loss during propagation, and their diffraction ability is extremely weak, making them highly susceptible to obstruction and communication interruptions. To overcome these propagation defects, reconfigurable intelligent metasurface (RIS) technology has emerged.

[0003] Traditional RIS systems can only serve users on the same side as the transmitter. To address this limitation, researchers have proposed STAR-RIS technology, extending the communication range to 360 degrees. Simultaneously, with the comprehensive expansion of human activities into the ocean, the demand for high-speed data exchange from underwater observation networks and deep-sea operation platforms is increasingly urgent. Underwater wireless optical communication can be seen as a technological extension of terrestrial free-space optical communication to underwater channels. Existing research on the combination of STAR-RIS and THz is extensive, but research on the performance of STAR-RIS-assisted underwater wireless optical communication (UWOC) is insufficient, and there is also a lack of security performance analysis of combining terrestrial and underwater communication. Therefore, this invention studies the security performance of STAR-RIS-assisted THz-UWOC. Summary of the Invention:

[0004] This invention provides a STAR-RIS-assisted THz-UWOC security performance analysis method to address the problems existing in the prior art. It enables more accurate analysis of STAR-RIS-assisted THz-UWOC security rates.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a STAR-RIS-assisted THz-UWOC system security performance analysis, the steps of which are as follows:

[0006] S1: Establish a system model for STAR-RIS-assisted THz-UWOC, considering a single-antenna access point (AP), a UAV configured with STAR-RIS, and a surface buoy relay (V). t and Vr Legitimate users U1 and U2, an eavesdropping user Eve, and a friendly jammer. The eavesdropping user eavesdrops on the legitimate users' information, and the jammer emits signals to interfere with the eavesdropping user.

[0007] S2: In the first stage, the AP transmits the signal as follows: Where P A Let s be the transmit power at AP. k k∈{1,2} is the transmitted signal, a k For transmission to user U k The power allocation coefficient; the signal is transmitted to the relay V. i The signal received at i∈{t, r} is represented as Among them, h i and h ar For THz channel vectors, It is the STAR-RIS phase coefficient matrix, β i This represents the amplitude coefficient of a STAR-RIS element. For STAR-RIS phase shift, n si The hardware impairment follows a complex Gaussian distribution. k si Represents hardware damage parameters, n i The Gaussian white noise at the relay point satisfies Relay V i Decoding k The signal-to-interference-plus-noise ratio (SINR) is

[0008] S3: The second-stage relay achieves cross-medium conversion from THz signals to underwater wireless optical signals, then at user U k U can be obtained at this location k Decodes k SINR is And Eve Decodes at the eavesdropping user k SINR is Where P R It is the transmission power at the relay point, P j It is the jammer's transmission power, g rk and g re Let g be the underwater optical channel coefficient. jk and g re Let K and K be the channel coefficients from the jammer to user k and the eavesdropper, respectively, with index k=1. When k=2, Noise power here Hardware damage coefficient Self-interference cancellation coefficient ε e ∈[0,1];

[0009] S4: Based on relay V t and V r Optimal relay selection is performed using partial channel information, i.e. Among them, V i The instantaneous signal-to-noise ratio (SNR) at the location is Therefore, the instantaneous SNR at the optimal relay point is γ. * =max(γ) t γ r After selection, the SINR at the relay point can be re-expressed as...

[0010] S5: γ can be obtained from the statistical characteristics of the THz channel. * Cumulative distribution function Depend on and γ * The relationship can be used to calculate its cumulative distribution function. in g l,rk The path loss coefficient is given; the cascaded channel gain Y can be obtained based on the statistical characteristics of underwater optical channels. rk cumulative distribution function Therefore γ k The cumulative distribution function can be expressed as The cumulative distribution function is in g l，re and g l，je The path loss coefficient can be obtained using Gauss-Laguerre numerical integration. Approximate expression;

[0011] S6: Considering half-duplex relay, the achievable rate for a legitimate user to decode its own information is: make Its cumulative distribution function can be obtained; then using Using the Gauss-Chebyshev integral approximation of the cumulative distribution function, the approximate closed-form expression for the safe rate of user k can be obtained as follows: in N p It is the order of the Chebyshev polynomial, υ q The zeros of a Chebyshev polynomial of order q are denoted as υ. q =cos((2q-1)π / (2N) p Thus, the system security and rate formulas are obtained as follows:

[0012] The present invention has the following beneficial effects: The present invention studies the security performance of STAR-RIS assisted THz-UWOC, takes into account the impact of hardware damage and jammers, and obtains an approximate expression for the system security rate, providing an effective method for performance evaluation and security and rate calculation of similar systems. Attached image description:

[0013] Figure 1 This is a diagram illustrating the analysis steps for the safety performance of the STAR-RIS-assisted THz-UWOC of this invention.

[0014] Figure 2 This invention presents curves showing the changes in safety and rate of transmission power with different numbers of STAR-RIS elements.

[0015] Figure 3 This invention presents curves showing the changes in safety and rate with transmit power under different exponential generalized gamma (EGG) distribution parameters. Detailed implementation method:

[0016] The invention is further described below with reference to the accompanying drawings.

[0017] I. System Model

[0018] Consider a single-antenna access point (AP), a drone (UAV) configured with STAR-RIS, and a surface buoy relay (V). t and V r Legitimate users U1 and U2, an eavesdropping user Eve, and a friendly jammer. The eavesdropping user is listening to the legitimate users' information. The jammer is transmitting signals to interfere with the eavesdropping user. The AP to STAR-RIS and STAR-RIS to relay channels are modeled as THz channels. in These represent large-scale fading and small-scale fading, respectively.

[0019] The channels relayed to legitimate users and eavesdroppers, and the channels from jammers to legitimate users and eavesdroppers, are called underwater optical channels, represented as follows:

[0020] g w =g l，w g t，w g p,w (1)

[0021] Where: w∈{r1,r2,re,j1,j2,je},g l，w For underwater path loss, g t，w Modeled as an exponential generalized gamma EGG distribution, g p，w This indicates pointing error.

[0022] The first phase AP transmission signal is Among them, P A s represents the transmit power at the AP. k k∈{1,2} is the transmitted signal, a k For transmission to user U k The power allocation coefficient. The signal is transmitted to the relay V. i The signal received at i∈{t, r} is represented as in It is the phase matrix of STAR-RIS, β i This represents the amplitude coefficient of a STAR-RIS element. n is the phase shift coefficient. si Hardware damage, subject to The complex Gaussian distribution, k si Represents hardware damage parameters, n i The Gaussian white noise at the relay point satisfies Relay V i Decoding sk The signal-to-interference-plus-noise ratio (SINR) is:

[0023]

[0024] Where: when the index k = 1, When k = 2,

[0025] The second-stage relay station performs cross-medium conversion from THz signals to underwater wireless optical signals, enabling user U... k The received signal is: The signal received by user Eve during the eavesdropping is as follows: Where P R It is the transmission power at the relay point, s j For the signal sent by the jammer, n sk n se For hardware damage, n k n e For Gaussian white noise, here: noise power Hardware damage coefficient Self-interference cancellation coefficient ε e ∈[0, 1]. User U k And Eve's Decoding k The SINR can be represented by the following distribution:

[0026]

[0027] II. Statistical Channel Analysis

[0028] Based on V t and V rThe optimal relay selection is based on partial Channel State Information (CSI). Specifically, it involves estimating V... t and V r The maximum instantaneous signal-to-noise ratio is determined by the fading channel coefficients, and this strategy is expressed as:

[0029]

[0030] Where V t The instantaneous signal-to-noise ratio (SNR) at point SNR is expressed as: Therefore, the instantaneous SNR at the optimal relay point is γ. * =max(γ) t γ r After selection, the SINR at the relay point can be re-expressed as...

[0031] Based on the statistical characteristics of the THz channel, γ * Cumulative distribution function for:

[0032]

[0033] in It is an incomplete gamma function with shape parameter . The rate parameter is δ k Related to the path loss of the THz channel. Due to γ * and The relationship can be obtained cumulative distribution function in Based on the statistical characteristics of underwater optical channels, the cascaded channel gain Y can be obtained. rk cumulative distribution function for:

[0034]

[0035] Where ω1, λ1, a1, b1, c1 represent the parameters of the EGG distribution. It is the Meijer-G function. Therefore, γ can be obtained. k cumulative distribution function as well as cumulative distribution function in An approximate expression can be obtained using Gauss-Laguerre numerical integration, namely:

[0036]

[0037] in It is the cumulative distribution function, x iIt is an nth-order Laguerre polynomial L n The n roots of (x), That is the corresponding weight, N L It is the order.

[0038] III. Safe Rate Analysis

[0039] Considering half-duplex relay, first calculate the achievable rate at which a legitimate user decodes its own information.

[0040]

[0041] make Its cumulative distribution function can be obtained as follows:

[0042]

[0043] use The cumulative distribution function can be used to further derive the safe rate for legitimate users, written as:

[0044]

[0045] Let t = 2x / τ k -1, using substitution, can be transformed into an integral over the interval [-1, 1], and then calculated.

[0046]

[0047] The approximate expression can be calculated using the Gauss-Chebyshev integral approximation closed-form solution as follows:

[0048]

[0049] in N p It is the order of the Chebyshev polynomial, υ q The zeros of a Chebyshev polynomial of order q are denoted as υ. q =cos((2q-1)π / (2N) p Thus, the system security and rate formulas are obtained as follows:

[0050] The following evaluation uses computer simulation to assess the STAR-RIS-assisted THz-UWOC security performance analysis method and rate calculation. The distance between the AP and STAR-RIS is set as d. ar =5m, STAR-RIS to relay V t and V r Let the distances be d respectively. t =20m,d r =15m, the distance from the relay to the legitimate user is d1=d2=100m, and the distance to the eavesdropping user is de =200m, the distance from the jammer to the eavesdropping user is d je =60m, STAR-RIS element count M is set to 42, noise power The order of the Gaussian Laguerre polynomial is set to N. L =50, the order of the Gauss-Chebyshev polynomial is N. p =150, self-interference cancellation coefficient ε e =1, P j =P r The pointing error coefficient ζ = 0.8863. Specific simulation parameters are shown in the table below:

[0051]

[0052] Figure 2 This demonstrates that in a STAR-RIS-assisted THz-UWOC communication system, the system's security and rate of transmission increase with the total transmit power P. s The increasing trend of STAR-RIS element counts was analyzed, and the performance differences under different STAR-RIS element counts M were compared. The figures show that when M is 24, 42, and 64, the simulation results closely match the theoretical results, proving the accuracy of the theoretical calculation formula. Furthermore, with the increase of transmit power, the security and rate of all curves show a rapid upward trend, indicating that increasing transmit power effectively improves channel quality and increases the secure transmission rate. In addition, the number of STAR-RIS elements has a significant impact on system performance. At the same transmit power, the larger the value of M, the higher the system's security and rate. This is because a larger number of STAR-RIS elements enhances the received signal strength of legitimate users, thereby improving system security.

[0053] Figure 3 The curves depicting system safety and rate of return as a function of transmit power are presented, including cases with different EGG distribution parameters and pointing error coefficient ζ. With increasing transmit power, the overall safe rate of return significantly improves, and the Monte Carlo simulation results are in high agreement with the theoretical curves, thus verifying the effectiveness of the system model in complex underwater channels. Different combinations of EGG parameters represent different levels of underwater turbulence, affecting system performance. A slight channel attenuation is observed in the scenario of ω1 = 0.4589, achieving a higher safe rate. A decrease in the ζ value leads to a significant drop in the overall safe rate of return, indicating that beam pointing error caused by turbulence or platform jitter increases, hindering legitimate channel alignment and safe transmission.

[0054] In summary, the performance analysis method proposed in this invention can effectively analyze the security performance and security and rate calculation of the STAR-RIS-assisted THz-UWOC system, and the simulation results fully demonstrate its effectiveness.

[0055] The above description is only a preferred embodiment of the present invention. It should be noted that modifications and improvements made to the present invention by those skilled in the art without departing from the basic principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for analyzing the security performance of a reconfigurable smart metasurface STAR-RIS-assisted terahertz underwater wireless optical communication (THz-UWOC) capable of simultaneous transmission and reflection, characterized in that... Includes the following steps: Step s1: Establish the system model of STAR-RIS assisted THz-UWOC, consider a single-antenna access point AP, a UAV equipped with STAR-RIS, a water buoy relay V r and V r , a legal user U1 and U2, an eavesdropping user Eve and a friendly jammer, the eavesdropping user eavesdrops on the information of the legal user, and the jammer transmits signals to interfere with the eavesdropping user; Step S2: In the first stage, the AP transmits the signal as follows: Where P A Let s be the transmit power at AP. k k∈{1,2} is the transmitted signal, a k For transmission to user U k The power allocation coefficient; the signal is transmitted to the relay V. i The signal received at i∈{t, r} is represented as Where h i and h ar This is the terahertz (THz) channel vector. It is the STAR-RIS phase matrix, β i This represents the amplitude coefficient of a STAR-RIS element. n is the STAR-RIS phase shift coefficient. si The hardware impairment follows a complex Gaussian distribution. k si Represents hardware damage parameters, n i The Gaussian white noise at the relay point satisfies Relay V i Decoding k The signal-to-interference-plus-noise ratio (SINR) is Step S3: In the second stage, the relay station performs cross-medium conversion from THz signal to underwater wireless optical signal, then at user U... k U can be obtained at this location k Decodes k SINR is And Eve Decodes at the eavesdropping user k SINR is Where P R It is the transmission power at the relay point, P j It is the jammer's transmission power, g rk and g re Let g be the underwater optical channel coefficient. jk and g je Let K and K be the channel coefficients from the jammer to user k and the eavesdropper, respectively, with index k=1. When k=2, Noise power here Hardware damage coefficient Self-interference cancellation coefficient ε e ∈[0,1]; Step S4: Based on relay V t and V r Optimal relay selection is performed using partial channel information, i.e. Among them, V i The instantaneous signal-to-noise ratio (SNR) at the location is Therefore, the instantaneous SNR at the optimal relay point is γ. * =max(γ) t γ r After selection, the SINR at the relay point can be re-expressed as... Step S5: γ can be obtained based on the statistical characteristics of the THz channel. * Cumulative distribution function Depend on and γ * The relationship can be used to calculate its cumulative distribution function. in g l，rk The path loss coefficient is given; the cascaded channel gain Y can be obtained based on the statistical characteristics of underwater optical channels. rk cumulative distribution function Therefore γ k The cumulative distribution function can be expressed as The cumulative distribution function is in g l，re and g l,je The path loss coefficient can be obtained using Gauss-Laguerre numerical integration. Approximate calculation expression; Step S6: Considering half-duplex relay, the achievable rate for a legitimate user to decode its own information is: make Its cumulative distribution function can be obtained; then using Using the Gauss-Chebyshev integral approximation of the cumulative distribution function, the approximate closed-form expression for the safe rate of user k can be obtained as follows: in N p It is the order of the Chebyshev polynomial, υ q The zeros of a Chebyshev polynomial of order q are denoted as υ. q =cos((2q-1)π / (2N) p Thus, the system security and rate formulas are obtained as follows:

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